1. Field of the Invention
The present invention relates to a technology for embedding data into image data.
2. Description of the Related Art
A technology for embedding invisible data into digital data or printed images, in other words, digital watermarking technology has been developed. However, image quality degrades when data is embedded into a printed image by the digital watermarking technology.
In the digital watermarking technology disclosed in Japanese Patent Laid-Open Publication No. 2004-512751 and Japanese Patent No. 3589111, complexity of an image area in which data is embedded is analyzed based on a standard deviation or a frequency component of the image area. Based on the complexity, embedding strength (for example, degree of change in grayscale values of the image) of data is controlled, thereby preventing degradation of image quality of the printed image.
In the digital watermarking technology disclosed in Japanese Patent No. 2003-78756, localized complexity of the image is computed and embedding strength of data is modified according to the localized complexity to prevent degradation of image quality.
However, in the conventional technology, image quality of the image having embedded data degrades as compared to the original image.
To be specific, when embedding data into an image by using the conventional technology, complexity of the image area in which data is to be embedded is analyzed, and embedding strength is controlled according to the complexity only. Due to this, data is embedded indiscriminately into an image area such as a white image area that suffers a degradation of image quality even due to a minute change in grayscale values, thereby resulting in degradation of the image quality.